1. Field of the Invention
The present invention relates to piezoelectric motors, and more specifically to piezoelectric torsional vibration driven motors.
2. Description of the Prior Art
The use of piezoelectric ceramic materials such as lead zirconate titanate (PZT) is well known for applications for sensors, transducers, actuators, and other electromechanical devices.
Many actuators have been developed using electroactive materials, including the torsional actuator disclosed in U.S. Pat. No. 6,020,674. This torsional actuator uses an even number of alternately poled segments of electroactive material that are arranged side by side. The segments are bound together in an integral structure, with conductors positioned between adjacent segments. Under an applied electric field, the torsional actuator produces large angular displacement and a high torque. Similarly, a torsional piezoelectric actuator is described in Glazounov et al., xe2x80x9cPiezoelectric Actuator Generating Torsional Displacement from Piezoelectric d15 Shear Responsexe2x80x9d, Appl. Phys. Lett. 72, pages 2526-2528, 1998.
For some applications, a large rotational motion with a large torque output is demanded. For example, vibration and noise control systems for helicopter rotor blades require an actuator that can provide large amplitude rotational motion with a high torque.
Piezoelectric ultrasonic motors have been developed using traveling wave and standing wave theories that provide higher torque density than electromagnetic motors. An example of the current art in piezoelectric motor technology is provided in Glenn et al., xe2x80x9cDevelopment of a Two-Sided Piezoelectric Rotary Motor for High Torquexe2x80x9d, SPIE 3041, 1997. These piezoelectric ultrasonic motors are of limited application, however, because they have either lower power density or lower efficiency than conventional electromagnetic motors.
U.S. patent application Ser. No. 09/697,716, incorporated herein by reference, discloses a torsional motor comprising the actuator of U.S. Pat. No. 6,020,674, a rotor, and one or two one-way clutches. The one-way clutches transmit angular displacement of the actuator to the rotor such that the rotor rotates in a single direction. The use of a single one-way clutch produces a half-cycle torsional motor. The use of two one-way clutches produces a full-cycle torsional motor. The half-cycle torsional motor transmits the angular displacement of only one end of the actuator. The full-cycle torsional motor also transmits the angular displacement of the other end of the actuator. Thus, the full-cycle torsional motor produces about double the rotary speed (rpm) as the half-cycle torsional motor at the resonance condition. U.S. patent application Ser. No. 09/697,716 discloses the use of a single rotor.
U.S. patent application Ser. No. 10/113,640, incorporated herein by reference, discloses the use of a second set of one-way clutches for reversing the direction of rotation of the rotor. The rotor is a helical shaft for pumping. The shaft rotates one direction or the other depending on which set of clutches is engaged.
There remains a need for a compact, simple, lightweight dual-rotor motor, which uses a torsional actuator as a stator, providing high torque density, high power density, and high efficiency in response to an alternating electric field.
It is an object of the invention to provide a piezoelectric dual-rotor motor with high torque density, high power density, and high efficiency.
It is an object of this invention to provide a compact and lightweight piezoelectric motor.
It is an object of this invention to provide a simple piezoelectric motor, which converts an alternating electric field to torsional vibration and directly into rotary motion.
It is an object of this invention to provide a full-cycle piezoelectric torsional vibration motor.
These and other objects are achieved by a torsional motor, comprising a plurality of segments comprising an electroactive material having a poling along the length dimension of each segment arranged in the shape of a tube; a plurality of conductors disposed between adjacent segments; two or more one-way clutches, and two rotors, whereby the angular displacements of the tube are transmitted to the rotors.